Ultrafine BaPb_1-xBi_xO₃ powders prepared by the spray-ICP technique

Abstract

Ultrafine powders of a trnary oxide system, Ba−Pb−Bi−O, were prepared by spraying aqueous mixed solutions of Ba(NO₃)₂, Pb(NO₃)₂, and Bi(NO₃)₃ into an argon inductively coupled plasma of ultrahigh temperature above 5000 K (the spray-ICP technique). Phases of the powders were largely dependent on the powder collectors enclosing the tail flame and its successive gas flow. In the water-cooled collector, mixtures of amorphous and crystalline materials were formed. In the collector where the gas flow was spontaneously maintained at about 550°C by ICP itself, ultrafine BaPb_1−xBi_xO₃ (BPBO) 10–40 nm in particle diameter was obtained. The BPBO thus obtained had a few wt.% of water and carbonate. They were lost by heat treatment up to 550°C, and a single-phase BPBO was formed. The as-prepared BPBO (x=0.25) showed no superconducting transition down to 1.5 K, but the one having a particle diameter of ∼ 1 μm formed by heating the as-prepared BPBO up to 1000°C had a superconducting transition temperature at 11.3 K.